Amazonite

Amazonite, also known as amazonstone, is a green tectosilicate mineral, a variety of the potassium feldspar called microcline. Its chemical formula is KAlSi3O8, which is polymorphic to orthoclase. The name is derived from the Amazon River, from which green stones were once believed to have been obtained, although it remains uncertain whether those stones were actually amazonite. Although amazonite has been used for jewellery for more than three thousand years, as evidenced by archaeological finds in Middle and New Kingdom Egypt and Mesopotamia, it is not mentioned by any ancient or medieval sources. It was first described as a distinct mineral in the 18th century. Green and greenish-blue varieties of potassium feldspars that are predominantly triclinic are designated as amazonite. It has been described as a "beautiful crystallized variety of a bright verdigris-green" and as possessing a "lively green colour". It is occasionally cut and used as a gemstone.